1. Field of the Invention
The present invention relates to a technology for control of power switch.
2. Description of the Related Art
A power switching device, such as a circuit breaker, has a problem that reignition occurs during operation of breaking a small capacitive current, such as a charging current in an unloaded power line or a load current in a capacitor bank. One conventional approach for preventing such reignition is to operate the power switching device at high speed before the recovery voltage reaches its crest value, i.e., for approximately 10 milliseconds, when the power switching device interrupts current. As a result, insulation recovery can be achieved before the recovery voltage rises.
For example, Japanese Patent Application Laid-open No. 2004-55420 discloses a conventional circuit breaker in which a movable contact is coupled to a switch driving mechanism through a cam mechanism, which moves the movable contact at relatively high speed at an early stage of opening stroke of the movable contact. Accordingly, the movable contact can be moved at relatively high speed only in necessary part of its full stroke, and does not need to be moved at high speed throughout the full stroke. As a result, energy for driving the movable contact can be lowered, and the size of the circuit breaker can be reduced.
With the conventional circuit breaker, however, a coupling mechanism including the cam mechanism needs to be arranged between the movable contact and the switch driving mechanism. Therefore, the circuit breaker is necessitated to be of complex configuration, making it difficult to simplify the switch driving mechanism. Furthermore, because a large force is applied to the coupling mechanism during operation, the cam mechanism needs to be composed of rigid members, and thereby the cost and the size of the circuit breaker increase.
Although the conventional circuit breaker can be operated while there is no reignition, it is a single-phase circuit breaker capable only of separately interrupting a current flow in each phase.